Neutronic analysis of candidate accident-tolerant cladding concepts in pressurized water reactors

Abstract

A study analyzed the neutronics of alternate cladding materials in a pressurized water reactor (PWR) environment. Austenitic type 310 (310SS) and 304 stainless steels, ferritic Fe-20Cr-5Al (FeCrAl) and APMT TM alloys, and silicon carbide (SiC)-based materials were considered and compared with Zircaloy-4. SCALE 6.1 was used to analyze the associated neutronics penalty/advantage, changes in reactivity coefficients, and spectral variations once a transition in the cladding was made. In the cases examined, materials containing higher absorbing isotopes invoked a reduction in reactivity due to an increase in neutron absorption in the cladding. Higher absorbing materials produced a harder neutron spectrum in the fuel pellet, leading to a slight increase in plutonium production. A parametric study determined the geometric conditions required to match cycle length requirements for each alternate cladding material in a PWR. A method for estimating the end of cycle reactivity was implemented to compare each model to that of standard Zircaloy-4 cladding. By using a thinner cladding of 350 µm and keeping a constant outer diameter, austenitic stainless steels require an increase of no more than 0.5 wt % enriched 235 U to match fuel cycle requirements, while the required increase for FeCrAl was about 0.1%. When modeling SiC (with slightly lower thermal absorption properties than that of Zircaloy), a standard cladding thickness could be implemented with marginally less enriched uranium (~ 0.1%). Moderator temperature and void coefficients were calculated throughout the depletion cycle. Nearly identical reactivity responses were found when coolant temperature and void properties were perturbed for each cladding material. By splitting the pellet into 10 equal areal sections, relative fission power as a function of radius was found to be similar for each cladding material. FeCrAl and 310SS cladding have a slightly higher fission power near the pellet's periphery due to the harder neutron spectrum in the system, causing more 239 Pu breeding. An economic assessment calculated the change in fuel pellet production costs for use of each cladding. Implementing FeCrAl alloys would increase fuel pellet production costs about 15% because of increased 235 U enrichment and the additional UO 2 pellet volume enabled by using thinner cladding.

Iron-chrome-aluminum alloy cladding for increasing safety in nuclear power plants

“…By its own nature, FeCrAl alloys offer a larger parasitic neutron absorption compared to zirconium alloys [6,7,22]. Because FeCrAl alloys such as APMT and C26M are stronger than zirconium alloys at near 400°C, the FeCrAl material for the cladding can be made approximately half the thickness of the current zirconium alloys (Figs.…”

Assessment of Neutronic Characteristics of Accident-Tolerant Fuel and Claddings for CANDU Reactors

“…Meanwhile, SiC cladding has a better neutron economy than zircaloy, but if the cladding must be made significantly thicker, the reduced fuel volume may lead to higher enrichment requirements [23]. Overall, the use of steel cladding is expected to increase fuel costs [23].…”

“…For a pressurized water reactor (PWR), if the FeCrAl clad thickness can be reduced to 300 m, an increase in enrichment can be avoided without impacting the cycle length, due to increased uranium loading from the use of larger fuel pellets [23]. Meanwhile, SiC cladding has a better neutron economy than zircaloy, but if the cladding must be made significantly thicker, the reduced fuel volume may lead to higher enrichment requirements [23]. Overall, the use of steel cladding is expected to increase fuel costs [23].…”

Neutronic Analysis of the Candidate Multi-Layer Cladding Materials With Enhanced Accident Tolerance for Wwer Reactors

“…Many of the recent papers and reports focused on neutronic performance of ATF fuel concepts for traditional PWR and BWR reactors [8][9][10][11]. However, the ATF fuels can and should be employed also in the WWER reactors that are in operation in the Czech Republic, Bulgaria, Slovakia, Hungary, Finland, Ukraine, India, and Russia.…”